Current DAVx⁵ versions require Android 4.4 or later. Older Android versions are not supported anymore, but can you use old DAVx⁵ versions which were compatible with Android <4.4. However, all DAVx⁵ versions require Android 4 or later.
Older DAVx⁵ versions work with Android <4.4, but there is no support and there won't be any updates, including security updates. We strongly recommend to update your Android device to Android 4.4 or later (maybe using a custom ROM) and use the latest version of DAVx⁵.
If you really need to install an old version of DAVx⁵, we recommend to install F-Droid and activate "F-Droid Archive" in the repositories (F-Droid / Settings / Repositories, see screenshot).
Then you can use an old version which is compatible with your device.
You may notice crashes and other misbehavior with latest formally compatible DAVx⁵ version because compatibility was not tested enough anymore. In this case, use an even older version, which should be compatible again.